Metal oxide nanoparticles are useful in a variety of technologically important applications. Nanoparticle deposition is expected to be a promising alternative to current thin-film deposition technologies for low-temperature fabrication of metal oxide films. Metal oxide nanoparticle-inks can be deposited using existing roll-to-roll or ink-jet systems to realize low-cost, low-waste, highly scalable and high-speed manufacturing. In the case of nanoparticle films, sintering at high temperature may not be required because the crystalline nanoparticles are formed during chemical production.
Although solution deposition of metal oxide nanoparticle-inks is a versatile and simple approach to depositing metal oxide films, the synthesis of metal oxide nanoparticles that are highly crystalline, monodisperse and precisely doped by a simple and reproducible general route remains a significant challenge. Metal oxide nanoparticles typically have been produced at high temperatures and under thermal decomposition conditions, and the synthesis parameters are difficult to control precisely. To achieve monodisperse nanocrystals, the reaction conditions are chosen to separate the nucleation and growth phases of the reaction. High temperatures are typically required to solubilize precursors, decompose the precursors, and/or convert (anneal) amorphous nanoparticles to the crystalline form. For example, monodispersed metal oxide nanoparticles have been synthesized by thermal decomposition or pyrolysis of metal organic precursors at temperatures greater than 300° C. (Park et al., Ang. Chemie, 46:4630-60 (2007); Jana et al., Chemistry of Materials, 16:3932-3935 (2004)). Extended reaction and aging times are often required to attain crystalline nanoparticles, and uniform doping or production of mixed oxide nanocrystals can be difficult because each metal precursor has a different decomposition temperature. The production of core/shell structures is challenging under these conditions because nucleation of new particles from the shell precursor competes with shell growth onto the core material. Finally, high temperatures preclude the use of thermally-sensitive organic chemical functionality within stabilizers and ligands.
Metal oxide nanoparticles also have been formed by alcoholysis and aminolysis of metal precursors (Park et al., Ang. Chemie, 46:4630-4660 (2007); Narayanaswamy et al., JACS, 128:10310-9 (2006); Gilstrap et al., Adv. Mat., 20:4163-6 (2008)). However, these methods still use reaction temperatures above 290° C.